Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：Springer Nature Singapore  

Ocean thermal energy conversion (OTEC) is a system that produces clean energy from the temperature differences in the ocean. Its power production is very stable and is expected to be implemented as a base-load power supply, despite using a natural energy source. In addition, this energy source would provide an attractive integration with other industries such as aquaculture with ocean nutrient enhancement, desalination, deep seawater cooling, and hydrogen production. Currently, a floating OTEC plant is in development toward a commercial-scale deployment. The floating plant is configured with a floating platform, mooring system, seawater intake pipe/inlet, and discharge pipe/duct. In particular, a cold water pipe (CWP) is the most challenging component in a commercial-scale OTEC. For a 100 MW-scale CWP, the length is 600–1000 m, and the diameter is over 10 m, designed to transport deep seawater at a flow rate of approximately 200 m3/s. Due to its size, there is a strong dynamic coupling between the floating platform and the mooring system, requiring a coupled analysis and an integrated design approach with other components. Meanwhile, one of the authors of this paper has proposed a 100 MW-net OTEC plantship for Indonesia, which utilizes a converted pre-owned ship to reduce capital costs. In this paper, a coupled dynamic analysis is performed for the preliminary design of the mooring system and CWP, along with a sensitivity analysis of the dynamic responses of the floating platform and CWP to design parameters. The results are used to discuss the dynamic characteristics and design methods for an OTEC floating plant, to improve reliability and further develop this floating structure concept.

DOI： 10.1007/978-981-97-0495-8_36

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：American Society of Mechanical Engineers  

Abstract

A water intake pipe/riser is an important component in deep seawater utilization technologies. Regarding the issue of flow-induced vibration, the concern of instability due to the internal flow has received considerable interest. A key question, particularly in the water-aspirating pipes, is the effect of the inlet flow on the dynamics. This study experimentally investigates the internal flow and inlet effects on the dynamics of a hang-off water intake pipe under top-end excitations. The results indicate that the internal flow effect increases inline response. In particular, it suggests the existence of a bifurcation phenomenon, where the amplitude significantly increases under excitation at slightly shorter periods than the natural period. The experiments further compare different inlet shapes: bellmouth, T-shape and L-shape; however, no significant differences in their response characteristics are observed. The second part of this paper provides a discussion based on CFD simulations stressing the contribution of the contracted jet formed inside the pipe and the sink flow in the vicinity outside the inlet to the dynamics of the water intake pipes.

DOI： 10.1115/OMAE2024-124537

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Language：Others   Publishing type：Research paper (other academic)  

Abstract

A cold water intaking pipe/riser is an important component of a floating Ocean Thermal Energy Conversion (OTEC) plant. Its dynamics subject to the large intake flow rate of seawater and motion excitation from a platform have not been definitively understood. This study experimentally investigates the dynamics with two experimental setups. The first setup uses a controllable pump and 4 m long pipe to investigate instability. The second setup uses a high capacity pump to investigate instability and forced vibration subject to top harmonic excitation. The results are compared with an analytical model considering the inlet flow effect. The analytical model predicts that a water intake pipe does not lose stability at any high flow velocity. The experiment newly confirmed that the pipe keeps stable up to 5.5 m/s which is the maximum velocity attainable in this experiment. The experiment and analytical model also highlight that a high internal flow velocity significantly increases the amplitude of inline vibration. Furthermore, the experiment also takes a new look on the dynamics such as long-period vibration and transverse vibration.

DOI： 10.1115/omae2023-103375

Language：Others   Publishing type：Research paper (scientific journal)   Publisher：Journal of Fluids and Structures  

Dynamic stability due to internal axial flow is a considerable problem for a pipe conveying fluid such as deep seawater intaking for an Ocean Thermal Energy Conversion (OTEC) plant. However, there has been much ambiguity about its dynamics, and this raises a question about whether such an aspirating pipe submerged in water flutters or not. Therefore, the objective of this paper is to provide an experiment to take a new look at the dynamics of pipe aspirating fluid (water). The experimental apparatus is constructed to eliminate expected disturbances, and we measure free damped vibrations of a submerged 4 m length pipe with internal flow. As a result, we observe the nonlinear and non-planar behavior, however, the pipe converges to the zero point and remains stable at a maximum velocity of 1.66 m/s. Subsequently, we review existing theoretical models, and present a comparison with the results from the tank experiment. In addition, we provide a new model of the inlet flow field, which plays an important role on stability, considering the flow separation and jet formed inside of the pipe entrance. This equation is solved by FEM for time integration and eigenvalue analysis, and the results seem to reproduce the experimental natural period and amplitude of the free vibration with internal flow. The model also suggests that an aspirating pipe submerged in water does not flutter up to the maximum flow velocity attainable in the experiment.

DOI： 10.1016/j.jfluidstructs.2022.103789

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Language：Others   Publishing type：Research paper (other academic)   Publisher：Proceedings of the International Conference on Offshore Mechanics and Arctic Engineering - OMAE  

A commercial-scale Ocean Thermal Energy Conversion (OTEC) floating plant will be attached a large diameter Cold Water Pipe (CWP). There are concerns about unstable vibration and changes in the dynamic characteristic due to too large mass flow rate. Since the vibration may interfere development of larger capacity plant, comprehending the phenomena have generated considerable interest. The main objective of this study is to confirm whether the theory that describes the vibration of submerged fluid-conveying pipe reproduces the real phenomena through a tank experiment. We construct the experiment eliminated possible disturbances, and the free damping vibration of polycarbonate pipe of 4 m length is measured during water intake. In order to compare the experimental pipe and theoretical models, the damping characteristics are identified from the results without internal flow. As a result of the comparison, although the theoretical model using the inlet end condition reproduces basically reproduced the experiment, we observe a three dimensional nonlinear behavior that could not be predicted by the theory. We believe that this experiment will serve to improve the theories.

DOI： 10.1115/OMAE2022-78136

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Event date： 2024.12

Language：English   Presentation type：Oral presentation (general)  

Venue：Hong LKong   Country：Hong Kong  

Event date： 2024.8

Language：English   Presentation type：Oral presentation (general)  

Venue：Tokyo   Country：Japan  

Event date： 2023.6

Language：Others   Presentation type：Oral presentation (general)  

Country：Australia  

Abstract

A cold water intaking pipe/riser is an important component of a floating Ocean Thermal Energy Conversion (OTEC) plant. Its dynamics subject to the large intake flow rate of seawater and motion excitation from a platform have not been definitively understood. This study experimentally investigates the dynamics with two experimental setups. The first setup uses a controllable pump and 4 m long pipe to investigate instability. The second setup uses a high capacity pump to investigate instability and forced vibration subject to top harmonic excitation. The results are compared with an analytical model considering the inlet flow effect. The analytical model predicts that a water intake pipe does not lose stability at any high flow velocity. The experiment newly confirmed that the pipe keeps stable up to 5.5 m/s which is the maximum velocity attainable in this experiment. The experiment and analytical model also highlight that a high internal flow velocity significantly increases the amplitude of inline vibration. Furthermore, the experiment also takes a new look on the dynamics such as long-period vibration and transverse vibration.

Event date： 2023.6

Language：Japanese  

Country：Other  

Theoretical and Experimental Investigation on Dynamic Response of a Pipe Aspirating Fluid

Event date： 2022.10

Language：Others  

Country：Other  

A commercial-scale Ocean Thermal Energy Conversion (OTEC) floating plant will be attached a large diameter Cold Water Pipe (CWP). There are concerns about unstable vibration and changes in the dynamic characteristic due to too large mass flow rate. Since the vibration may interfere development of larger capacity plant, comprehending the phenomena have generated considerable interest. The main objective of this study is to confirm whether the theory that describes the vibration of submerged fluid-conveying pipe reproduces the real phenomena through a tank experiment. We construct the experiment eliminated possible disturbances, and the free damping vibration of polycarbonate pipe of 4 m length is measured during water intake. In order to compare the experimental pipe and theoretical models, the damping characteristics are identified from the results without internal flow. As a result of the comparison, although the theoretical model using the inlet end condition reproduces basically reproduced the experiment, we observe a three dimensional nonlinear behavior that could not be predicted by the theory. We believe that this experiment will serve to improve the theories.

Language：Japanese   Publishing type：Research paper, summary (national, other academic conference)  

Language：Japanese   Publishing type：Research paper, summary (national, other academic conference)  

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Language：Japanese   Publishing type：Research paper, summary (national, other academic conference)  

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Language：Japanese   Publisher：日本船舶海洋工学会  

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CiNii Research

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Language：Japanese  

CiNii Books

CiNii Research

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